Experimental Physics and
Industrial Control System

[email protected] (William Lupton) · Wed, 21 Jan 1998 09:38:10 -1000

Dear all,

  When I posted yesterday, I wasn't thinking about CA links but Andy's
table and Ralph's summary are really interesting and clarified things
for me. I was wrong when I said that the put did not cause the record to
process.

  I went back to look what my problem _really_ is. When a DB output link
is processed, two quite independent things happen:

  a) the value is put and monitors are posted if the destination field
     is not .VAL or the target field PP attribute is FALSE

  b) the target record is processed if the destination field is .PROC or
     the link from the source record is PP and the target record is
     passive

  In my case, the link from the source record is PP, PP of the target
field (a calc's .VAL field) is NO and the link type is DB, so, by (a)
above, a monitor is posted with the value which has just been put to
.VAL, and by (b), the target record is processed, which may post
_another_ monitor on .VAL, with a different value from the first. This
is exactly what I saw.

  I'm not sure whether this is actually a problem or whether I've just
done something stupid. However, the fact remains that if the PP of the
target field had been YES, the problem would not have occurred, which
brings me back to my original question of why some .VAL fields have
the PP attribute set to NO.

  Thanks,

  William

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System